Typically soluble silver and halide salts are reacted in an aqueous dispersing medium containing a peptizer to form radiation-sensitive silver halide grains. The grains are separated from each other physically and held in suspension by the peptizer. Occasionally a small percentage of the grains are observed to aggregate, but these grain aggregations are easily removed by filtration before the emulsion is coated.
Mignot U.S. Pat. No. 4,334,012 discloses a method for precipitating fine silver halide grains in the absence of a peptizer. Mignot avoids grain aggregation in the absence of a peptizer by limiting the concentration of soluble salts to less than 0.1 mole per liter (M/L). At higher salt concentrations, typical of those used in precipitating silver halide grains in the presence of a peptizer, uncontrolled grain aggregation occurs in the absence of a peptizer, rendering the resulting composition uncoatable and unsuitable for imaging applications.
Levy U.S. Pat. No. 5,512,426 departs from the ordinary practice of silver halide emulsion manufacture in that the formation of dispersed grain clumps is sought as an alternative to the conventional practice of keeping individual grains separated from one another in the dispersing medium. Levy precipitates fine silver halide grains in an aqueous dispersing medium that does not contain a peptizer. To avoid uncontrolled grain aggregation Levy, like Mignot, teaches working with dilute dispersions. Specifically, Levy teaches maintaining silver concentrations below 0.1 M/L. The fine grains are chemically sensitized and then aggregated into dispersed clumps having a mean equivalent circular diameter (ECD) of up to 10 .mu.m. Peptizer is then added to stabilize the dispersion of the clumps.